Electrical measuring instrument



Oct. 29, 1940. w. H owE 2,219,942

ELECTRICAL MEASURING INSTRUMENT Filed March 30, 1939 ITWV6TTCOT: 9 7Wifliam H.1Qovve,

v v by His Attorney Patented Oct. 29, 1940 PATENT OFFICE ELECTRICALMEASURING INSTRUMENT William H. Itowe, Lynn, Mass, assignor to GeneralElectric Company, a corporation f New York Application March 30, 1939,Serial No. 264,924

4 Claims.

of the device and presses the pointed prods into the terminals of thecells thereby causing a discharge of current through the resistor. Thereading of the. voltmeter under such circumstances provides anindication of the condition of the cell. If such a device is to besuitable for universal application in testing various sizes of storagebatteries wherein the spacing between the terminals or poles of theindividual cells is variable over a wide range, it must be soconstructed that the prods are relatively movable to alter the spacingbetween the contact points.

Furthermore, the resistor element should be positioned in such a mannerthat the operator will not suffer injury from burns caused by contactwith theresistor when it is heated due to the battery discharge currentduring the testing operation. It is further desirable that the apparatusbe simple and reliable in operation and .of a rugged and inexpensiveconstru tion.

An object of my invention is to provide an improved testing instrumentin which the spacing between the contact points may be altered in asimple and reliable manner.

Another object of my invention is to provide an improved battery testinginstrument wherein the spacing between the prods or contact points isadjustable to render the device particularly adaptable for theexamination. and testing of j storage batteries in which the spacingbetween the terminals of the individual cells of the different batteriesis variable over a wide range.

.A further object of my invention is to provide an improved portabletesting instrument built as 50 a unitary structure which is of simpleand rugged construction and which may be manufactured and assembled inan economical manner.

A-still further object of my invention is to provide an instrument ofthe abovecharacter 55 wherein the operator is protected from burninjuries caused by direct contact with the resistor which becomes heateddue to the passage of heavy current during the testing operation orcycle.

In accordance with my invention in its pre- 5 ferred form I mount eachof the prods of the testing device in separate longitudinal bores orholes in the body portion and provide means whereby one of the prods maybe rotated about an axis in the bore so that the spacing between m thecontact points may be made adjustable over a wide range. A handle,formed in general as a hollow cylinder, functions as a skirt dependingfrom the body portion, and provides an inner chamber for enclosing thehelical resistance element which encircles the upper end,of the testingprods and which is connected between the prods. The condition of thecellis indicated by observing the reading of a voltmeter connected m tomeasure the voltage drop across the resistor when the contact points areapplied to the terminals of the cell under test.

My invention will be-better understood from the following descriptionwhen read in conjunc- 25 tion with the accompanying drawing, and itsscope will be pointed out in the appended claims. Fig. 1 is anelevational view in cross section of one form of apparatus which may beused in carrying out my invention; and Fig. 2 is a cross 30 sectionalview of the apparatus taken along the line II of Fig. 1 and illustratesthe movable prod adjusted to an intermediate position for varyingthespacing between the contact points.

The same reference characters are employed to designate correspondingparts illustrated by the several views of the drawing.

Referring to Fig. 1 of the drawing, the numeral ll designates the bodyportion of the device which may be made of wood, molded textolite, orother suitable insulating material, and from which extends a handle inthe form of a skirt or depending portion I2 and an upper flange-likeannular projecting portion I3. I prefer to make 5 these parts as anintegral structure and in the illustration shown theyare formed as asingle unit by a molding process. The body portion II is provided withtwo longitudinalholes or passageways I4 and IS. The testing prods l6 andI1, formed of a suitable electrically conducting material, comprisesubstantially straight or extended portions generally designated by thenumeral l8, and these prods are bent outwardly from a point beginningnear the bottom of the skirt or handle to form the oflset or curvedportions l3, thereby producing a divergent arrangement of the lowersection of the prods with reindicated at 20.

spect to the upper straight portions II. The prods are then bent back ata point intermediate their extremitiesso that the free ends are arrangedin substantially parallel relationship as The free extremities of theprods are sharpened or pointed as at 2| to engage the battery cellterminals 22 and 23, or the terminals of other apparatus across whichthe potential is to be measured.

I provide means. for connecting the prods in supported relation to thebody portion ll of the testing device. In the arrangement illustrated,

the upper ends or extended portions of the prods l6 and I! are eachprovided with a reduced diameter portion 24 and 25. The portion 25 isadapted to serve'as a bearing journal and each portion is adapted toextend into the separate holes or passageways l4 and I5, respectively,of the body portion By virtue of this reduced diameter portion ashoulder 26 is provided on each of the prods. A washer 21 is adapted to,slide over the reduced diameter portion of each upper surface 30 of thebody portion ll.

over the end of the prod and the nuts 32 are screwed down to applypressure for maintaining the washers 21 and 23 in frictional engagementwith the surfaces 28 and-30, respectively.

. top nut 32 on the prods functions as a locking nut to maintain thedesired pressure or adjustment. It will, of course, be understood thatthe frictional engagement between the prods and the support or bodyportion may be secured by the omission of the washers described, but Iprefer to employ the washers or their equivalent in order to distributethe frictional pressure over a greater area.

The supporting means described above permits relative rotation of theprods l6 and I! whereby the straight portion 20 may move in a circulararc to adjust the spacing between the contact points 2|. This featurerenders the device particularly adaptable for those testing operationsin which the spacing. between the terminals of storage battery cells orthe spacing between other electrical circuit points to be examined issubject to wide variations. Referring to both figures of the drawing, inthe arrangement illustrated I provide a notch or depression 33 about theinner surface of the handle portion l2 which, for convenience as well assimplicity, may be formed by means of the integral ribs or projections34 attached to the handle portion l2. To aid in the description of theapparatus at' this point, I may conveniently refer to the prod l6 as thefixed vprod, although my invention is not necessarily limited thereto,and the prod 'li'l as the movable, are describing, or rotatable prod.Each of the prods is provided with a transversely disposed opening 35which is adapted to receive the reduced diameter shank 36 of each of thepins 31. The portion 38 of larger cross-section thus forms a shoulderwhich abuts against the outer surface of the prods. The pins 31 arerigidly attached The to theprods by peening. or riveting the ends asshown at 39. The larger diameter portion 38 of the fixed prod I6 isadapted to rest in the notch or depression 33 and is thus firmly heldagainst rotary movement.

Considering now the structural arrangement of the means for providingthe, are describing movement of the contact portion 2| in a given plane,I provide a rib or projecting portion which is similar to theprojections 34 already descrlbed'and which may be formed in a similarmanner. The projecting portion 40 provides a stop against which the pin31 abuts and prevents rotational movement in a clockwise direction butleaves the prod l1 free to rotate in a counterclockwise direction aboutits axis in the longitudinal hole or passageway IS. The prod may thus berotated to an intermediateposition as indicated by the dotted portion atI'm to vary the spacing between the contact points 2| and thus make thedevice adaptable for testing various sizes of batteries wherein thespacing of the cell terminals is subject to wide variations. Thefrictional engagement of the washers 21 and 29 with the lower and uppersurfaces 28 and 30, respectively, of the body portion provides means formaintaining the rotatable prod IT in any given intermediate position towhich it is moved.

-An important feature of the above described construction is that theelevation of all portions of the movable prod remains the same for allpositions to which it may be rotated. Or stated in a different way, ifthe body portion and one of the prods is maintained in a given positionand the movable prod rotated relatively thereto, the contact portions ofthe. prods will always intersect a common plane regardless of thespacing between the contacts. In the preferred arrangement, the point ofthe are describing prod,

for any given adjustment, lies in a plane which is substantiallyperpendicular to and contains" the point of the fixed prod.

In order to simulate actual service conditions of the cell to beexamined, a flexible resistance element 4| in theform of a helicalribbon -is positioned within the chamber 42 formed by the handle portionl2 and is connected to the prods l6 and I! at the points 43 and 44 bywelding or other suitable means. The handle I 2 thus prevents theoperator from suffering physical injury due to direct contact with theresistance element in its heated condition. The helical resistanceelement 4| is adapted to encircle the straight or extended portions l8of the prods and this construction together with the flexibility offeredby such a resistance element enables the prod IT to rotate relative tothe fixed prod l6. a 4

portion I3. The casing may be secured to the' portion |3 by screws 49 orother suitable means.

The voltmeter or indicating instrument is further I provided witha-flange portion 50 which is adapted to rest on the upper end of thecasing 41. A

ring 5| of angular cross section is adapted to fit over the flange andfrictionally engage the edge of the flange and the outer surface of thecasing as shown at 52. This provides a means of simple construction forpositioning the voltmeter and maintaining its contacts or terminals 46in firm engagement with the upper ends of the prods.

The method of assembly of the apparatus should be apparent from theforegoing description. With the casing and voltmeter removed, the prodsl6 and IT, with resistor 4| attached as shown and with the washers 21 inthe proper position, are inserted in the passageways l4 and,

I5, care being taken to position the pin 31 of the prod I6 in the notch33 and the pin 31 of the prod H on the proper side of the projection 40as shown in Fig. 2. The washers 29 and 3| are placed over the ends ofthe prods and the nuts 32 are then screwed down to produce the desiredfrictional pressure between the surfaces of the washers and the bodyportion. The voltmeter is then inserted in position and the apparatus isready for use.

To operate the device it is merely necessary to move the rotatable prodIT to give the desired spacing between the contact points 2|, grasp thehandle l2 to hold the contact points in engagement with the cellterminals, and observe the indication of the instrument 45 during thecurrent discharged through the resistor.

The advantages to be derived from practicing my invention are notlimited to those applications involving the examination of storagebattery cells but it may also be found useful in those cases where it isdesired to measure the potential between a plurality of points, such forexample, as occurs in checking switchboard circuits and the like. Insuch a case the helical resistance element 4| is dispensed with and thevoltmeter 45 must be one suitable to the potential range likely to beencountered.

While I have described the principle of operation of my inventiontogether with the apparatus which I now consider to represent the bestembodiment thereof, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from myinventiori, and I, therefore, aim in the appended claims to cover allchanges and modifications as fall within the true spirit and scopeof myinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A battery testing device comprising a body portion having a holetherein, a pair of prods connected to said body portion, one of saidprods having its supported portion extending into said hole andjournaled for rotation therein, a resistance element connected to saidprods and encircling portions thereof, a voltmeter provided withresilient terminals, and means for maintaining said terminals inengagement with said prods.

2. A battery testing device comprising a body portion having a holetherein, a pair of prods connected to said body portion, one of saidprods having its supported portion extending into said hole andjournaled for rotation therein, and a voltmeter provided with resilientterminals, said terminals adapted to frictionally engage said prods.

3. A battery testing device'comprising a body portion having asubstantially vertical passageway therethrough, a pair of prods securedto said body portion, one of said prods having its supported portionextending into said passageway and journaled for rotation therein, ahelical resistance element wound about said prods and electricallyconnected across said prods, and a voltage measuring instrumentelectrically connected to read the potential drop across said resistanceelement.

4. A battery testing device comprising a body portion having an aperturetherein, a pair of contact prods connected to said body portion, one ofsaid prods having its supported portion extending into said aperture andjournaled for rotation therein, said rotatable prod having its contactportion ofiset with respect to its supported portion whereby the spacingbetween the contacts of said prods is varied upon rotation of saidrotatable prod, and a helical resistance element encircling portions ofsaid prods and electrically connected across said prods.

WILLIAM H. ROWE.

